Overview of the tensile strength and flexural strength of aluminium sheets

Aluminium sheets are indispensable in modern industrial sectors. Whether in mechanical engineering, vehicle construction or in the manufacture of fixtures – their combination of lightness, corrosion resistance and mechanical load-bearing capacity makes them a versatile material. Two key characteristics are particularly relevant for technical applications: tensile strength and flexural strength.

What does tensile strength mean for aluminium sheets?

Tensile strength describes the maximum resistance that a material can oppose to a tensile load before fracture occurs. For aluminium sheets, this value refers to the load in the longitudinal direction, i.e. to a purely axial tensile stress. The material is stretched, and the tensile strength indicates the stress at which the specimen fails.

For aluminium sheets, this value depends on the alloy, the manufacturing process, the sheet thickness and the heat treatment. The microstructure – for example the ratio of crystal structure to grain size – can also play a role. In industrial practice, aluminium sheets are frequently used in a heat-treated condition (e.g. T6 or H111) in order to achieve specific strength values. The usual units are megapascals (MPa) or newtons per square millimetre (N/mm²), whereby both units of measurement are equivalent.

Example values for common aluminium alloys:

Alloy	Tensile strength Rm (MPa)
EN AW-5083 H111	approx. 275 MPa
EN AW-6082 T6	approx. 310 MPa
EN AW-7075 T6	approx. 540 MPa

These values apply to standard sheets at room temperature and under standard conditions (in accordance with DIN EN ISO 6892-1).

What does flexural strength indicate?

Flexural strength describes the maximum mechanical stress that a material can withstand during bending before it tears or is permanently deformed. In technical usage, the term flexural tensile strength is also frequently used, in particular for standardised test methods such as the 3-point bending test.

Typical factors influencing flexural strength:

• Alloy and microstructure
• Sheet thickness
• Bending radius
• Direction of the bending stress (rolling direction vs. transverse)

Here too, typical guide values can be given:

Alloy	Flexural strength (MPa)
EN AW-5083	approx. 215–240 MPa
EN AW-6082	approx. 240–270 MPa
EN AW-7075	approx. 450 MPa

Why are these characteristics decisive?

Tensile strength and flexural strength are key characteristics when it comes to the mechanical design of constructions using aluminium sheets. They significantly influence the decision as to whether a material is suitable for a particular stress. Particularly in an industrial environment, where high forces, dynamic loads or repeated bending operations occur, it is decisive that the material used reliably withstands them over the entire service life.

Too low a tensile strength value can lead to failure under tensile stress – for example in components that are subjected to tension or preloaded. Insufficient flexural strength, in turn, can lead to sheets deforming under load or even cracks forming. Safety also plays a role: in many applications, knowledge of the material limits is a prerequisite for compliance with standards and safety requirements.

Designers and planners must take these values into account during dimensioning, for example through safety factors or targeted reinforcement measures. The selection of the suitable aluminium alloy is therefore not merely a comparison of numerical values, but part of a holistic material strategy.

Tensile strength vs. flexural strength: where is the difference?

Although both terms describe mechanical stresses, they act in different load directions:

• Tensile strength: Purely axial load in the longitudinal direction
• Flexural strength: Combination of tension and compression on the upper and lower side of the sheet during bending

In practice, bending stress is often more critical, since local material weaknesses can carry more weight here. When the bending limit is exceeded, aluminium tends to form cracks more quickly than to undergo plastic elongation.

Test methods and standards

Standardised methods apply for determining the mechanical properties. The most important standards are:

• DIN EN ISO 6892-1 – tensile test at room temperature
• DIN EN ISO 7438 – bending test (3-point or 4-point bending)

The results depend on the test speed, specimen dimensions and the direction of the stress. For reliable material selection, manufacturer-specific material data sheets should therefore always be used.

Applications in practice

The choice of the suitable aluminium sheet depends heavily on the field of application and the types of load occurring there. In practice, different alloys are used – depending on whether high strength, good formability or corrosion resistance is required.

EN AW-5083 is used above all where good bending properties, excellent corrosion resistance and weldability are required – for example in shipbuilding, in fixture construction or for large-area covers in mechanical engineering. This alloy is also very well suited for use in damp environments or outdoors.

EN AW-6082 combines medium strength with good machinability and is therefore predestined for components in mechanical and plant engineering. Both tensile and bending stresses frequently occur here, for example in support plates, holders or frame elements.

EN AW-7075 offers extremely high strength values, but limited weldability. This alloy is preferably used in aircraft construction, for highly stressed tools and in motorsport engineering – wherever every gram of weight counts and at the same time the highest mechanical strength is required.

Aluminium sheets are also frequently used in mould making and automation technology when a combination of rigidity, dimensional accuracy and machinability is required. In these areas, specially milled precision sheets offer additional advantages with regard to flatness and tolerances.

Conclusion

The tensile strength and flexural strength of aluminium sheets are key characteristics for industrial material selection. Depending on the requirement, aluminium alloy, sheet thickness and type of stress should be carefully matched to one another. Only in this way can a reliable, long-lasting and safe application in design be realised.